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LELAND  STANFORD  JUNIOR  UNIVERSITY  PUBLICATIONS 


STUDIES  IN  ELECTRICITY 

.   1 


SOME  OBSERVATIONS 


UPON  THE 


CONDUCTIVITY  OF  A  COPPER  WIRE 


IN    VARIOUS    DIELECTRICS 


BY 


FERNANDO    SANFORD,  M.  S. 

Professor  of  Physics  in  the  Leland  Stanford  Junior  University 


PALO  ALTO,  CALIFORNIA 

PUBLISHED  BY  THE  UNIVERSITY 

1892 

PRICE,   FIFTY   CENTS 


LELAND  STANFORD  JUNIOR  UNIVERSITY  PUBLICATIONS 


NO.  1.  THE  TARIFF  CONTROVERSY  IN  THE 
UNITED  STATES,  1789-1833.  With  a  Summary 
of  the  Period  before  the  Adoption  of  the  Constitution. 
By  ORRIN  LESLIE  ELLIOTT,  Ph.D.  pp.  272.  Price,  $1.00. 

NO.  2.  SOME  OBSERVATIONS  ON  THE  CON- 
DUCTIVITY OF  A  COPPER  WIRE  IN  VARIOUS 
DIELECTRICS.  By  FERNANDO  SANFORD,  M.  S. 
pp.  44.  Price,  50  cents. 


ADDRESS 

THE   REGISTRAR, 

Palo  Alto,  California. 


LELAND  STANFORD  JUNIOR  UNIVERSITY  PUBLICATIONS 


STUDIES  IN  ELECTRICITY 


SOME  OBSERVATIONS 

UPON  THE 

CONDUCTIVITY  OF  A  COPPER  WIRE 

IN   VARIOUS    DIELECTRICS 


BY 

FERNANDO    SANFORD,  M.  S. 

Professor  of  Physics  in  the  Leland  Stanford  Junior  University 


PALO  ALTO,  CALIFORNIA 

PUBLISHED  BY  THE  UNIVERSITY 

SEPTEMBER,  1892 


SOME  OBSERVATIONS 

UPON   THE 

CONDUCTIVITY  OF  A  COPPER  WIRE 

IN    VARIOUS    DIELECTRICS 


It  is  probable  that  no  known  electrical  phenomenon 
offers  greater  difficulty  of  explanation  at  the  present  time 
than  the  phenomenon  of  metallic  conductivity.  Faraday 
has  given  reasons  for  believing  that  it  is  essentially  re- 
lated to  the  phenomenon  of  static  induction,  and  Maxwell's 
theory  would  make  both  phenomena  alike  dependentupon 
an  elastic  fluid,  or  ether,  which  permeates  both  the  con- 
ductor and  the  dielectric  around  it.  According  to  this 
view,  an  electric  charge  consists  of  a  displacement  of  this 
elastic  fluid,  which,  on  account  of  its  elasticity,  tends  to 
return  to  its  original  position,  while  a  current  consists  of 
a  displacement  of  this  same  fluid  throughout  the  entire 
length  of  a  closed  conducting  circuit,  in  which  case  the 
tendency  to  return  to  its  original  position  does  not  appear. 
It  would,  accordingly,  appear  that  this  electric  elasticity 
of  the  ether  disappears  in  conductors,  or  at  the  bounding 
surface  between  conductors  and  dielectrics.  Since  appar- 
ently the  same  inducing  force  may  induce  different 
charges  in  different  dielectrics,  it  seems  necessary  to 
assume  that  the  elasticity  of  the  ether  varies  in  different 
dielectrics.  Since,  also,  the  ether  displacement  for  a  given 
force  will  be  inversely  as  its  elasticity,  it  follows  that  the 

3 


4  SOME    OBSERVATIONS    UPON    THE 

specific  inductive  capacity  of  a  dielectric  will  be  pro- 
portional to  the  reciprocal  of  the  elasticity  of  the  ether  in 
this  dielectric  when  subjected  to  electric  stress. 

It  is  now  well  known  that  light  waves  are  caused  by 
electric  stresses  in  this  same  ether,  and  it  seems  necessary 
to  assume  that  they,  too,  depend  upon  this  same  electric 
elasticity,  and,  accordingly,  that  a  fixed  relation  should 
exist  between  the  velocity  of  light  in  a  dielectric  and  the 
specific  inductive  capacity  of  the  dielectric.  This  relation, 
as  determined  by  Maxwell  and  Helmholtz,  would  make 
the  optical  index  of  refraction  proportional  to  the  square 
root  of  the  dielectric  constant.  While  it  is  true  that  this 
relation  has  not  been  extensively  verified  by  experiment, 
it  is  also  true  that  different  determinations  of  the 
dielectric  constant  have  given  very  different  results  for 
the  same  substance. 

So  far  as  I  am  aware,  it  has  been  assumed  that  the 
electric  conductivity  of  a  wire  or  other  metallic  conductor 
is  uninfluenced  by  the  nature  of  the  dielectric  in  its  field 
of  force,'  and  depends  only  upon  the  nature  and  temper- 
ature of  the  conductor.  The  close  relation  which  seems 
to  exist  between  the  current  in  a  conductor  and  the  phe- 
nomenon of  induction  in  a  dielectric,  and  the  apparent 
fact  that  the  ether  displacement  in  a  conductor  carrying 
a  current  is  caused  by  a  lateral  stress  communicated  to  it 
by  the  ether  in  the  dielectric  surrounding  the  conductor, 
has,  however,  made  it  seem  to  me  probable  that  the  amount 
of  this  displacement  for  a  given  force  might  also  be  modi- 
fied by  the  nature  of  the  surrounding  dielectric,  or  that 
the  conductivity  of  a  given  wire  might  vary  in  different 
dielectrics. 

More  than  a  year  ago,  I  made  some  experiments  to  see 
if  this  phenomenon  of  variable  conductivity  could  be 


CONDUCTIVITY   OF    A   COPPER    WIRE  5 

observed,  but  with  only  negative  results.  Wishing  to  test  the 
matter  more  fully,!  had  made  a  piece  of  apparatus  by  means 
of  which  I  have  been  able  to  observe  the  suspected  pheno- 
menon in  liquid  and  gaseous  dielectrics,  and  by  means  of 
which  I  hope  to  accumulate  much  more  valuable  data 
concerning  the  action  of  dielectrics  upon  conducting 
wires. 

The  apparatus  used  consists  of  a  cylindrical  copper 
tube  120  cm.  long  and  2.5  cm.  in  internal  diameter.  The 
ends  of  the  tube  are  closed  air  tight  by  copper  plates, 
which  are  provided  with  stopcocks  for  filling  and  empty- 
ing the  tube.  To  the  inside  of  one  end  plate  is  fastened 
a  copper  wire  1  mm.  in  diameter,  which  passes  length  wise 
through  the  center  of  the  tube  and  out  through  an  insu- 
lated opening  in  the  other  end  plate,  where  it  is  soldered 
to  a  piece  of  lamp  cord,  made  of  many  small  wires,  by 
which  it  is  connected  with  the  Wheatstone's  Bridge. 
Another  similar  piece  of  lamp  cord  is  soldered  to  the  end 
of  the  tube  through  which  the  wire  passes,  and  is  likewise 
connected  with  the  bridge.  Midway  between  the  ends  of 
the  tube  is  another  tube  5  cm.  long  and  1  cm.  in  diameter 
entering  it  from  the  side.  This  tube  serves  to  admit  the 
thermometer  by  which  the  temperature  of  the  interior  of 
the  large  tube  is  measured. 

The  current  used  for  making  the  measurements  passes 
one  way  through  the  tube  and  returns  through  the  wire. 
By  this  arrangement,  the  entire  field  of  force  of  the  cur- 
rent to  be  measured  is  confined  within  the  tube,  and  the 
whole  of  the  dielectric  concerned  in  its  transmission  can 
be  changed  at  will. 

The  measurements  were  made  with  a  Hartmann  & 
Braun  combined  resistance  box  and  bridge,  with  bridge 
arms  of  1:1000.  The  smallest  resistance  used  was  .1  ohm, 


6  SOME    OBSERVATIONS    UPON    THE 

which  with  the  above  combination,  represented  a  resist- 
ance in  the  wire  and  tube  of  .0001  ohm.  The  galva- 
nometer used  is  the  physiological  galvanometer  of  DuBois 
Reymoiid,  manufactured  by  the  Geneva  Society  Construc- 
tion Company.  It  is  provided  with  a  concave  mirror  and 
ground  glass  scale,  and  the  usual  method  of  observing 
the  deflection  of  a  spot  of  light  reflected  from  the  mirror 
upon  this  scale  was  used.  This  deflection  was  plainly 
noticeable  for  a  change  of  resistance  corresponding  to 
.0001  ohm  in  the  wire  and  tube,  and  by  reversing  the 
current  several  times,  it  was  possible  to  obtain  a  deflection 
for  a  change  corresponding  to  one-fifth  of  the  above.  The 
measurements  were  accordingly  estimated  with  a  fair 
degree  of  accuracy  to  .00001  ohm.  As  the  combined 
resistance  of  the  wire  and  tube  was  about  .0335  ohm,  the 
average  of  any  set  of  measurements  was  certainly  not 
.03  of  one  per  cent  wrong.  The  zero  method  of  measure- 
ment was  adopted  throughout.  The  current  used  was 
obtained  from  a  battery  of  32  silver  chloride  cells,  usually 
through  100  ohms  resistance  between  the  battery  and  the 
bridge,  and  the  strength  of  current  through  the  wire  and 
tube  was  always  between  the  extremes  of  five  and  eight 
milli-amperes.  The  measurements  were  all  made  at  the 
temperature  of  the  room,  and  as  this  changed  very  slowly, 
only  a  few  measurements  could  be  made  in  a  day. 


CONDUCTIVITY    OF    A    COPPER    WIRE  7 

COMPARISON  OF  SOME  LIQUID  DIELECTRICS 
WITH  AIR. 

The  first  set  of  measurements  was  made  with  air  and 
wood  alcohol  as  dielectrics.  I  thought  that,  on  account 
of  the  high  specific  inductive  capacity  attributed  to  this 
liquid,  it  would  be  as  likely  as  any  to  give  results  differ- 
ing from  air.  In  this  I  was  disappointed.  After  draw- 
ing a  curve  representing  the  resistance  of  the  wire  at 
different  temperatures  in  air,  the  corresponding  curve  for 
wood  alcohol  was  found  to  practically  coincide  with  it. 

The  wood  alcohol  was  then  poured  out  of  the  tube,  but 
was  not  carefully  drained  off,  and  the  tube  was  filled  with 
petroleum.  An  increase  in  the  resistance  of  the  wire 
was  at  once  noticed.  Eleven  measurements  were  made 
with  this  dielectric  during  two  days,  March  4th  and  5th, 
the  liquid  being  poured  off  six  times  and  measurements 
made  in  the  air  in  the  meantime,  but  the  same  liquid 
being  poured  back  each  time.  The  curve  representing 
these  eleven  measurements  was  found  to  indicate  a 
resistance  .00008  ohm  greater  than  that  represented  by 
the  curve  for  the  air  readings.  As  the  average  resistance 
of  the  wire  and  tube  at  the  temperature  at  which  the 
measurements  were  made  was  about  .C3350  ohm,  this 
difference  represented  about  .27  of  one  per  cent  of  the 
whole  resistance.  It  was  noticed  that  the  liquid  had  a 
cloudy  appearance,  looking  neither  like  wood  alcohol  nor 
petroleum,  but  as  "the  wood  alcohol  had  caused  no  varia- 
tion in  the  resistance,  I  supposed  this  increase  of  resist- 
ance to  be  due  to  petroleum. 


8  SOME    OBSERVATIONS    UPON    THE 

On  the  following  day,  March  6th,  the  tube  having  been 
carefully  drained  out  and  dried  was  filled  with  pure 
petroleum  and  a  neAv  set  of  measurements  was  begun. 
These  indicated  at  once  a  decrease  of  resistance  in  the 
wire.  As  this  seemed  to  contradict  the  former  measure- 
ments, I  thought  that  some  of  the  contact  resistances 
about  the  apparatus  were  changing.  Measurements  were 
accordingly  made  at  irregular  periods  from  March  6th  to 
April  5th,  the  battery  and  galvanometer  being  detached 
and  used  for  other  purposes  and  the  apparatus  being 
allowed  to  stand  from  March  14th  to  28th.  In  all,  34 
measurements  were  made  in  air  and  22  in  petroleum,  the 
dielectric  in  the  meantime  being  changed  five  times,  and 
the  temperature  changes  being  from  13.6°  C.  to  26°  C. 
The  whole  series  was  entirely  consistent.  Not  a  single 
reading  made  with  the  wire  in  either  dielectric  crossed 
the  curve  for  the  other  dielectric.  The  average  difference 
in  the  resistance  of  the  wire  in  the  two  dielectrics  was 
.00006  ohm,  which  corresponds  to  about  .18  of  one  per 
cent  of  the  whole  resistance,  the  conductivity  of  the  wire 
being  that  much  greater  in  petroleum  than  in  air. 

The  curves  made  for  these  dielectrics  are  shown  in  Fig.  1. 

They  were  drawn  as  follows  :  The  points  representing 
the  resistance  at  the  different  temperatures  were  platted 
on  cross  section  paper,  none  of  the  points  for  either 
dielectric  being  omitted,  and  a  line  was  drawn  through 
them  with  a  pencil  and  ruler  as  nearly  as  possible  in  the 
true  direction  of  the  curve,  which  did  not  vary  percept- 
ibly from  a  straight  line.  The  distance  of  each  point 
from  the  line  was  then  measured,  and  the  algebraic  sum 
of  these  distances  divided  by  the  number  of  the  points 
taken  was  assumed  as  representing  the  true  distance  of 
the  curve  above  or  below  the  trial  curve  from  which 


CONDUCTIVITY    OF    A    COPPER    WIRE  9 

the  distances  were  measured.  The  final  curve  was 
then  carefully  drawn  parallel  to  the  other  curve  at  this 
distance  above  or  below  it,  as  the  conditions  required. 

The  above  measurements  made  it  seem  probable  that 
the  increased  resistance  with  the  first  petroleum  was  due 
to  the  wood  alcohol  which  was  mixed  with  it.  To  make 
this  certain,  the  petroleum  was  poured  off,  leaving  a  little 
in  the  tube,  and  the  tube  was  then  filled  with  wood  alcohol. 
Thirty-one  measurements  with  the  wire  in  this  liquid  were 
made  on  April  5th,  6th,  and  7th,  the  liquid  being  poured 
out  twice  in  the  meantime  and  twelve  measurements  made 
in  the  air.  The  thirty-one  successive  measurements  made 
for  the  liquid  represented  an  increase  of  resistance  over 
the  former  curve  made  for  air  of  .00007  ohm,  while  the 
twelve  air  measurements  averaged  only  .000004  ohm 
from  the  former  curve.  This  liquid,  which  consisted 
principally  of  wood  alcohol  and  contained  only  a  little 
petroleum,  gave  a  resistance  to  the  wire  .2  of  one  per  cent 
greater  than  it  had  been  in  air;  while  the  liquid  used  a 
month  before,  consisting  principally  of  petroleum  with 
only  a  little  wood  alcohol,  gave  an  increased  resistance  to 
the  wire  of  .27  of  one  per  cent. 

This  peculiar  effect  of  using  two  dielectrics  which  did 
not  seem  to, combine  with  each  other  was  observed  later 
with  wood  alcohol  and  benzine.  On  May  llth  and  12th 
another  series  of  five  measurements  was  made  with  wood 
alcohol  which  seemed  to  give  the  wire  an  increased 
resistance  of  .02  of  one  per  cent,  a  series  of  seven  meas- 
urements with  the  wire  in  benzine  gave  an  increased 
resistance  of  .06  of  one  per  cent,  and  a  series  of  nine 
measurements  when  the  tube  contained  nearly  equal  parts 
of  wood  alcohol  and  benzine  gave  an  increased  resistance 
of  .15  of  one  per  cent. 


10  SOME    OBSERVATIONS    UPON    THE 

The  other  liquids  tested  were  absolute  alcohol,  ordinary 
90  per  cent  alcohol,  carbon  bi-sulphide,  distilled  water, 
and  a  mixture  of  carbon  bi-sulphide  and  oil  of  turpentine. 

The  absolute  alcohol  gave  the  wire  an  increased 
resistance  over  air  of  .000064  ohm,  corresponding  to  .19 
of  one  per  cent  of  the  whole  resistance.  See  Fig.  2. 

The  measurements  for  90  per  cent  alcohol  were  more 
unsatisfactory  than  for  most  of  the  others  on  account  of 
a  much  wider  variation  than  usual  between  the  individ- 
ual measurements,  both  in  case  of  the  measurements  in 
alcohol  and  in  air.  These  measurements  were  made  in 
two  successive  days  from  once  filling  the  tube  with  alco- 
hol. Four  of  the  air  measurements  were  made  before  the 
alcohol  measurements  and  nine  were  made  afterwards. 
The  average  of  the  eight  measurements  in  alcohol  was 
greater  than  that  of  the  thirteen  in  air  by  .000024  ohm, 
but  the  irregularity  in  both  series  was  so  great  that  but 
little  value  should  be  attached  to  these  results.  The  cause 
of  this  irregularity  is  unknown  to  me. 

The  curve  for  carbon  bi-sulphide  differed  very  little 
from  that  made  for  air.  In  this  case,  the  air  curve  was 
made  before  filling  the  tube  with  the  carbon  bi-sulphide. 
Eleven  measurements  were  made  with  this  liquid  on  May 
9th  and  10th.  The  seven  measurements  made  on  the  9th 
all  indicated  a  decreased  resistance  in  the  wire,  though  of 
a  very  small  amount,  while  the  four  measurements  on  the 
10th  indicated  an  increased  resistance  of  a  somewhat 
greater  amount.  It  seems  probable  that  some  contact 
resistance  in  the  apparatus  had  increased  by  a  small 
amount  in  the  meantime. 

The  mixture  of  carbon  bi-sulphide  and  oil  of  turpen- 
tine gave  a  decreased  resistance  to  the  wire  of  about  .00003 
ohm,  or  nearly  .09  of  one  per  cent. 


CONDUCTIVITY   OF   A   COPPER    WIRE 


11 


With  distilled  water  the  irregularity  was  also  very 
great.  When  the  water  was  first  poured  in  it  seemed  to 
give  an  increased  resistance  to  the  wire,  but  this  increase 
seemed  to  disappear  slowly  as  the  water  continued  to 
stand  in  the  tube.  This  seemed  to  me  to  be  due  to  an 
increased  conductivity  of  the  water  caused  by  the  solu- 
tion of  salts  of  copper  from  the  wire  and  tube. 

The  following  tables  give  the  figures  relating  to  the 
different  measurements  as  preserved  in  my  note  book. 
It  will  be  observed  that  these  measurements  were  made 
at  all  times  of  the  day,  so  that  any  difference  of  tempera- 
ture between  the  wire  and  the  resistances  used  for  com- 
parison would  not  always  affect  the  result  in  the  same 
direction.  The  same  resistance  box  and  thermometer 
were  used  throughout. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

1892 
Feb.  22 

Air 

23.0 

.03385 

n 

12  M. 

it 

22.8 

.  03380 

a 

2  P.  M. 

l( 

25.0 

.03410 

ft 

5     " 

u 

25.2 

.03410 

Feb.  23 

9  A.  M. 

a 

19.1 

•03340 

u 

4  P.  M. 

it 

21.9 

.03370 

11 

6     " 

a 

23.0 

.  03385 

Feb.  24 

8.30  A.  M. 

\ 

it 

17.7 

.03320 

12 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE   IN 

OHMS 

Feb.  24 

10  A.  M. 

Air 

18.3 

.  03330 

It 

11.30  A.M. 

it 

20.0 

.03350 

tt 

3.15  P.M. 

a 

22.0 

.03370 

tt 

5 

it 

22.8 

.03383 

Feb.  25 

10  A.M. 

tt 

.  18.0 

.03327 

Feb.  26 

9.30  " 

it 

19.5 

.03347 

a 

3.20  P.  M. 

tt 

21.6 

.03368 

tt 

3.45     " 

Wood  Alcohol 

21.1 

.03366 

a 

5.20     " 

a 

21.7 

.  03367 

n 

9.00     « 

tt 

22.6 

.03377 

Feb.  27 

4.00     " 

tt 

21.0 

.03365 

Feb.  28 

9.30  A.M. 

tt 

18.0 

.03328 

Feb.  29 

10 

tt 

19.6 

.03343 

u 

2.30  P.  M. 

tt 

21.7 

.03370 

a 

6.00     " 

tt 

21.0 

.03360 

March  1 

4.00     " 

tt 

22.0 

.03374 

March  3 

10.30  A.M. 

it 

19.9 

.03350 

CONDUCTIVITY    OF    A   COPPER   WIRE 


13 


Poured  out  wood   alcohol  and  filled  with  petroleum. 
Some  wood  alcohol  left  in  the  tube. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

KESIST- 

ANCE   IN 

OHMS 

1892 
March  4 

ii 

Petroleum  and 

Wood  Alcohol 

a 

21.0 
22.0 

.03370 

.03385 

tt 

4.00  P.  M. 

it 

22.6 

.03388 

tt 

5.00     " 

it 

23.0 

.03392 

March  5 

9.00  A.  M. 

n 

17.7 

.03330 

u 

9.30     " 

Air 

19.0 

.03340 

a 

n 

9.45     " 
10.30  " 

Petroleum  and 
Wood  Alcohol 
Air 

19.1 
21.0 

.03347 
.03365 

u 

10.45  " 

Petroleum  and 
Wood  Alcohol 

20.0 

.03360 

Disconnected  apparatus  and  cleaned  tube  by  draining 
out  the  liquid  and  forcing  air  through  it  with  a  bellows. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

24.1 

RESIST- 
ANCE IN 
OHMS 

March  6 

7.45  p.  M. 

Air 

.03418 

"       7 

8.15A.M. 

tt 

21.0 

.03390 

a      tt 

9.30    " 

n 

22.0 

.03400 

14 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

March  7 

10.45  A.  M. 

Air 

23.1 

.03418 

li          it 

11.10    " 

a 

23.4 

.  03420 

(  i          a 

3.00  p.  M. 

a 

24.7 

.03431 

n          u 

3.50    " 

a 

25.0 

.03434 

a           a 

4.50    " 

t  i 

26.0 

.03442 

"       8 

9.15A.M. 

i  i 

19.9 

.03374 

u          u 

9.50    « 

i  . 

20.3 

.03383 

ii          « 

10.30    " 

a 

20.8 

.03384 

«          a 

11.45    " 

Petroleum* 

22.2 

.03390 

«          a 

12.15  p.  M. 

i  i 

22.0 

.03390 

a          u 

1.30    " 

u 

22.7 

.03400 

u          a 

2.10    " 

u 

23.0 

.03406 

a          u 

4.00    " 

ti, 

24.8 

.03426 

"      9 

9.00  A.  M. 

a 

20.0 

.03370 

u          a 

10.00    " 

a 

21  2 

.03386 

a          a 

11.15    " 

t  i 

21.7 

.03392 

«          u 

12.00   M. 

u 

22.0 

.03396 

u          a 

3.00  p.  M. 

a 

23.1 

.  03408 

*  Whittier,  Fuller  &  Go's.  150  °  Fire  Test  "  Star  "  Kerosene. 


CONDUCTIVITY   OF    A   COPPER    WIRE 


15 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

EESIST- 

ANCE    IN 

OHMS 

March  9 

5.00  P.  M. 

Petroleum 

24.0 

.  03415 

"     10 

10.00  A.  M. 

Air 

21.6 

.03392 

u      a 

11.00     " 

ti 

21.7 

.03394 

tl             It 

1.15  P.  M. 

u 

21.8 

.03395 

It         l( 

4.00    « 

n 

20.1 

.03374 

•«    11 

10.00  A.  M. 

n 

20.6 

.03382 

"     12 

2.10  P.  M. 

11 

19.1 

.03366 

"     13 

10.00  A.  M. 

it 

17.8 

.  03350 

n      a 

10.40    " 

it 

18.9 

.03360 

"     14 

10.00    <• 

11 

20.3 

.03380 

.   "     28 

10.45    " 

it 

16.3 

.03330 

a      a 

11.20    " 

it 

16.3 

.03330 

a      ti 

4.00  P.  M. 

ti 

17.0 

.  03340 

"     29 

10.30  A.  M. 

ti 

17.7 

.  03348 

"     30 

9.30    " 

it 

15.6 

.03325 

April  2 

2.00  P.  M. 

it 

17.9 

.  03349 

tt      tt 

2.10    " 

Petroleum 

18.9 

.03355 

it       u 

4.40    " 

ti 

17.7 

.  03343 

16 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  2 

5.30P.M. 

Petroleum 

17.6 

.  03340 

"       3 

9.50  A.  M. 

n 

13.6 

.03293 

n          u 

10.10    " 

a 

14.0 

.03298 

it           l( 

10.50     " 

1  1 

15.0 

.03310 

it           11 

12.10  P.  M. 

t  t 

16.6 

.03330 

(i           it 

5.40    " 

i  t 

16.6 

.03330 

"       4 

9.50  A.  M. 

Air 

15.1 

.03320 

n          u 

11.40     " 

« 

15.1 

.03315 

a           u 

4.00  P.  M. 

a 

18.9 

.03364 

a           tt 

4-10    " 

a 

18.9 

.03365 

u           u 

4.45     " 

t  ( 

19.2 

.03367 

u           u 

4.50    " 

i  i 

19.2 

.03367 

«           u 

5.30    " 

u 

19.3 

.03368 

u           u 

7.20    " 

Petroleum 

19.2 

.03364 

"       5 

8.30A.M. 

u 

13.6 

.03298 

a       a 

10.10     " 

a 

14.0 

.  03304 

a       a 

11.00    " 

1  1 

14.6 

.03310 

CONDUCTIVITY    OF    A    COPPER    WIRE  It 

The  curves  representing  the  above  measurements  for 
air  and  petroleum  are  given  in  Fig.  1. 

The  petroleum  was  mostly  poured  off  and  the  tube 
filled  with  Wood  Alcohol  at  11.35  A.  M. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  5 

12.00    M. 

Wood  Alcohol 
and  Petroleum 

14.8 

.03308 

«        it 

12.30  P.  M. 

tt 

15.3 

.03320 

<  .        t< 

1.45     " 

« 

16.4 

.03334 

i  '.       a 

3.00     " 

it 

17.6 

.03352 

a       a 

4.50     " 

it 

18.4 

.03363 

a       a 

5.30     " 

u 

18.9 

.03368 

a       it 

6.00     " 

11 

19.1 

.03368 

'    ft   :-  '  4< 

7.35     " 

it 

19.0 

.03364 

"      6 

8.30  A.  M. 

u 

16.1 

.03333 

<  >      it 

9.45     " 

i  , 

17.1 

.03345 

a      a 

10.45     " 

it 

18.3 

.03363 

a      a 

11.45    " 

tt 

18.7 

.03370 

U             (t 

12.35  P.  M. 

U 

19.0 

.03372 

(l             tl 

1.45     « 

(t 

19.5 

.03376 

t(         It 

3.30     " 

tt 

20.7 

.03395 

18 


SOME    OBSERVATIONS   UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  6 

4.40  P.  M. 

Wood  Alcohol 
and  Petroleum 

21.5 

.03405 

n      n 

5.30     " 

Air 

21.9 

.03395 

tl              it 

5.515     " 

tt 

21.6 

.03392 

it          It 

7.40     " 

a 

21.0 

.03386 

u          a 

9.20     " 

« 

15.3 

.03318 

u          u 

10.00    «' 

a 

18.6 

.03355 

7 

7.25  A.  M. 

a 

15.2 

.03316 

u          u 

9.15     " 

tt 

18.4 

.03355 

tt             U 

10.05     « 

tt 

19.0 

.03362 

tt          tt 

10.20     " 

Wood  Alcohol 

and  Petroleum 

18.0 

.03357 

tt          « 

10.50     " 

it 

18.9 

.03366 

tt          u 

11.30     " 

it 

19.1 

.  03368 

tt          a 

12.30  P.  M. 

i  i 

19.6 

.03373 

u         u 

1.45     « 

a 

20.0 

.  03381 

it,             U 

4.00     " 

Air 

23.0 

.03414 

n         u 

5.30     " 

a 

22.1 

.  03405 

tt         tt 

5.45     " 

a 

24.5 

.  03434 

it         a 

8.00     " 

u 

21.1 

.03390 

CONDUCTIVITY    OF    A   COPPER    WIRE  19 

It  will  be  noticed  that  the  first  measurement  after  pour- 
ing the  wood  alcohol  into  the  tube  which  had  just  con- 
tained the  petroleum  gave  the  same  resistance  that  the 
wire  had  shown  in  petroleum,  and  that  not  until  the 
fourth  measurement,  made  over  three  hours  after  the 
wood  alcohol  was  poured  in,  did  the  true  resistance  in 
the  mixed  liquid  seem  to  be  reached.  This  phenomenon 
was  frequently  observed  by  pouring  off  a  liquid  dielectric 
and  making  a  measurement  at  once,  and  in  nearly  every 
case  the  resistance  seemed  to  be  either  that  given  by  the 
liquid  dielectric  at  that  temperature,  or  one  between  that 
of  the  liquid  and  the  air  resistance  at  the  same  tempera- 
ture. From  this,  I  was  led  to  think  that  the  thin  layer 
of  this  dielectric  in  contact  with  the  wire  had  a  marked 
influence  upon  the  wire's  conductivity.*  For  this  reason 
when  the  liquid  was  poured  out  the  tube  was  usually 
carefully  drained  out  and  dried  by  blowing  air  through 
it  with  a  bellows  or  drawing  it  through  with  a  filter 
pump. 

After  the  last  measurement  in  air  given  above,  the 
tube  was  filled  with  ordinary  90  per  cent  alcohol,  and  the 
following  measurements  were  made. 

*  Since  the  above  was  in  type,  my  attention  has  been  called  to  the  re- 
marks made  by  Prof,  von  Helmholtz  before  the  recent  meeting  of  the 
British  Association  at  Edinburgh,  as  reported  in  "The  Electrician  "  of 
Aug.  12, 1892. 

The  substance  of  the  report,  so  far  as  it  applies  to  the  question  in 
hand,  is  that  a  mercury  column  in  a  glass  tube  may  have  a  greater  re- 
sistance due  to  the  film  of  air  adhering  to  the  inside  of  the  tube,  even 
when  the  thickness  of  this  film  does  not  exceed  .0005  of  a  wave  length 
of  light,  and  that  the  lowest  resistance  of  the  column  may  be  obtained 
by  allowing  a  drop  of  petroleum  to  spread  itself  over  the  inside  of  the 
tube.  It  has  seemed  to  me  possible  that  this  phenomenon  may  be  re- 
lated to  the  one  described  above. 


20 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  7 

9.20P.M. 

Alcohol 

19.0 

.03365 

"      8 

7.30  A.  M. 

it 

14.0 

.  03304 

(I             It 

8.40     " 

1  1 

15.1 

.03325 

11      S 

9.40     " 

i  i 

16.6 

.03341 

it          « 

10.50     " 

1  i 

17.9 

.03355 

tl          it 

12.30  P.  M. 

« 

19.0 

.03370 

<C              (I 

1.35     " 

it 

19.9 

.03381 

(I          it 

3.00     " 

it 

21.0 

.03395 

11            it 

4.05     " 

Air 

22.2 

.  03404 

((            it 

5.30     « 

n 

22.2 

.  03408 

It          tt 

8.00     " 

it 

21.0 

.  03394 

It         It 

10.00     " 

a 

20.0 

.  03376 

"      9 

7.30A.M. 

a 

15.6 

.03328 

((          (( 

8.40     " 

n 

16.3 

.  03339 

tl          It 

9.10     " 

a 

17.6 

.  03351 

tt          tt 

9.30     " 

1  1 

17.9 

.  03352 

tl        tl 

10.40     " 

i  i 

18.6 

.  03360 

CONDUCTIVITY    OF    A    COPPER    WIRE 


21 


Following  these  measurements  were  some  made  with 
gaseous  dielectrics  which  will  be  described  later.  On 
April  20th,  21st,  22d,  24th,  and  25th,  twenty-six  measure- 
ments were  made  in  air,  giving  the  curve  shown  in  Fig. 
2.  These  measurements  are  given  in  the  table  comparing 
air  and  illuminating  gas.  Directly  after  finishing  the  air 
and  gas  measurements  the  following  measurements  were 
made  in  absolute  alcohol,  and  were  compared  with  the 
air  curve  just  mentioned. 


DATE 

HOUR 

DlELECTEIC 

TEMP. 

RESIST- 
ANCE IX 
OHMS 

Absolute 

April  27 

2.50  P.  M. 

Alcohol 

18.4 

.03372 

it      n 

3.35     « 

n 

18.8 

.03377 

n      a 

4.25     " 

it 

19.3 

.03385 

n         it 

6.00     " 

ti 

19.9 

.  03390 

it         ti 

7.50     " 

it 

19.3 

.  03385 

"     28 

7.30A.M. 

n 

11.9 

.03300 

U              11 

8.20     " 

n 

13.9 

.03321 

tl        (t 

9.10     " 

n 

15.9 

.03343 

(t        11 

9.50     " 

n 

16.9 

.  03356 

tl          tl 

10.30     " 

n 

17.5 

.03364 

It          11 

11.30     « 

ti 

18.0 

.03368 

It             U 

12.10  P.M. 

n 

18.3 

.03373 

'      "   '     1.35     " 

it 

18.8 

.03377 

22 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

19.2 

RESIST- 
ANCE   IN 

OHMS 

April  28 

2.40  P.M. 

Absolute  Alcoh'l 

.03383 

n      a 

3.20     " 

« 

19.9 

.03392 

((      a 

6.10     " 

a 

21.0 

.03403 

li             It 

7.45     " 

u 

20.6 

.03400 

it          il 

7.30  A.  M. 

(i 

16.9 

.  03355 

"     29 

8.50     " 

n 

19.0 

.03380 

After  pouring  out  the  alcohol,  the  tube  was  left 
filled  with  the  vapor  of  alcohol  and  the  following  meas- 
urements were  made,  showing  that  the  resistance  returned 
to  practically  the  former  resistance  in  air. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

Air  and 

April  29 

9.50A.M. 

Alcohol  Vapor 

20.0 

.03388 

i  ( 

10.37     " 

n 

20.9 

.03398 

(I 

11.30     " 

u 

21.9 

.03410 

(( 

12.15  P.  M. 

1C 

22.2 

.03414 

11 

1.45      " 

11 

22.9 

.03423 

it 

4.00       " 

(I 

22.0 

.03412 

tl 

6.00      " 

tl 

20.6 

.03396 

(I 

8.08      " 

11 

18.5 

•03369 

CONDUCTIVITY    OF    A    COPPER    WIRE 


23 


On  May  6th,  a  new  series  of  air  measurements  was 
begun.  The  contacts  between  the  bridge  and  tube  had 
been  broken  off  and  re-soldered  in  the  meantime,  so  that 
no  comparison  can  be  made  between  these  measurements 
and  the  preceding. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  6 

2.35  P.  M. 

Air 

20.1 

.  03380 

It 

3.55     " 

tt 

19.4 

.03373 

it 

4.40     " 

« 

19.9 

.  03378 

It 

5.50     " 

a 

20.4 

.03385 

"      7 

7.30  A.M. 

it 

15.9 

.03329 

it 

9.00     " 

tt 

17.9 

.03353 

u 

4.00  P.  M. 

tt 

21.8 

.  03399 

« 

4.40     " 

u 

22.7 

.03412 

n 

5.30     " 

u 

23.3 

.03420 

tt, 

7.10     " 

11 

22.8 

.  03414 

11      8 

8.00  A.  M. 

tt 

13.4 

.03300 

a 

8.55     " 

(I 

14.9 

.03317 

Poured  in  about  a  spoonful  of  carbon 
allowed  to  stand  until  the  vapor  should 


bi-sulphide,  and 
fill  the  tube. 


24 


SOME    OBSERVATIONS    UPOJN    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

REfcilST- 
ANCE    IN 

OHMS 

May  8 

10.55  A.  M. 

Air  &  Carbon  Bi- 
sulphide Vapor 

17.2 

.03346 

"     9 

7.30     " 

« 

17.7 

.  03352 

a     u 

9.20     " 

u 

19.8 

.03377 

As  the  vapor  in  the  tube  seemed  to  cause  no  sensible 
deviation  from  the  measurements  in  air,  the  tube  was 
filled  with  ordinary  commercial  carbon  bi-sulphide  and 
the  following  measurements  were  made.  It  will  be  observed 
that  the  measurements  made  on  the  9th  all  indicate  a 
decreased  resistance  on  account  of  the  liquid,  while  those 
made  on  the  10th  indicate  an  increase.  As  some  meas- 
urements made  in  air  on  the  10th  also  indicate  an  increase, 
I  have  assumed  that  the  action  of  the  carbon  bi-sulphide 
upon  the  copper  wire  had  changed  its  resistance  by  about 
.00003  ohm,  which  seemed  to  be  about  the  amount  of  the 
permanent  change.  If  this  be  true, the  resistance  in  carbon 
bi-sulphide  is  slightly  less  than  in  air.  I  hope,  however,  to 
repeat  these  measurements  during  the  coming  year. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

Carbon  Bi- 

May  9 

10.25A.M. 

Sulphide. 

19.7 

.03373 

«       u 

11.30     " 

a 

19.8 

.03375 

tt       tt 

12.30  p.  M. 

tt 

20.0 

.03378 

CONDUCTIVITY   OF    A   COPPER   WIRE 


25 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  9 

1.55  P.  M. 

Carbon  Bi- 
Sulphide 

20.6 

.  03386 

«          u 

2.45     " 

a 

21.1 

.  03392 

«          « 

4.45     " 

(i 

22.0 

.03402 

«          (( 

6.00    " 

t( 

21.5 

.03397 

"    10 

7.30  A.  M. 

« 

17.3 

.03350 

«       « 

8.30    " 

M 

19.0 

.03370 

«          « 

9.00    " 

u 

19.8 

.03378 

u          u 

9.35    " 

a 

20.3 

.  03385 

May  llth  to  17th,  the  following  measurements  were 
made  with  air,  wood  alcohol,  benzine,  and  wood  alcohol 
and  benzine  mixed. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  11 

8.55  A.  M. 

Air 

15.6 

.03330 

u          « 

9.50    " 

a 

16.6 

.03343 

* 

11              U 

11.05    " 

u 

17.2 

.03352 

"     12.30  P.M. 

u 

19.2 

.03375 

26 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DlELECTRCC 

TEMP. 

RESIST- 
ANCE IN 

OHMS 

May  11 

2.15  P.M. 

Air 

20.5 

.03391 

It             tt 

4.15    " 

a 

22.0 

.03408 

tl             11 

5.35    " 

Wood  Alcohol 

21.9 

.  03407 

11            tt 

7.40     " 

n 

20.4 

.03390 

"     12 

7.25  A.M. 

tt 

13.4 

.03305 

a      u 

8.20    " 

it 

15.0 

.03323 

a      a 

9.15    " 

n 

16.0 

.03337 

a      u 

9.55    " 

Air 

17.2 

.03352 

a       it 

10.20    " 

Benzine 

17.3 

.03354 

tt       tt 

11.30    " 

a 

18.6 

.03367 

a       a 

2.15  P.M. 

it 

19.0 

.03372 

"     14 

7.30  A.  M. 

tt 

16.0 

.03337 

«       it 

8.30    " 

n 

16.9 

.03348 

tt       it 

12.35P.M. 

tt 

18.7 

.03370 

it       it 

2.00     " 

tt 

19.3 

.03378 

tt       it 

5.40     " 

n 

20.1 

.03390 

11     15 

9.05  A.  M. 

n 

15.9 

.03337 

CONDUCTIVITY    OF    A    COPPER    WIRE 


27 


Poured  out  about  half  of   the  benzine  and  replaced  by 
wood  alcohol. 


DATE 

HOUR 

DlELECTBIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  15 

2.00  P.  M. 

Benzine  and 
Wood  Alcohol 

20.2 

.03390 

a       (i 

7.30      " 

a 

20.2 

.03389 

"     16 

8.15  A.M. 

u 

16.0 

.03342 

K       K 

9.05     " 

It 

16.9 

.03352 

n          a 

10.00     " 

tl 

17.9 

.03363 

it          it 

12.00M 

it 

19.0 

.03377 

ti          n 

1.45  P.  M. 

(t 

19.8 

.03385 

It               (( 

3.30    " 

it 

20.9 

.  03397 

ti               It 

5.30     " 

it 

21.8 

.03410 

"     17 

9.50  A.  M. 

Air 

21.7 

.03405 

(i      (i 

12.20  P.  M. 

a 

22.9 

.03413 

11              It 

1.35     " 

n 

23.8 

.03430 

In  the  above  measurements  the  increase  of  resistance 
caused  ^y  mixing  the  two  dielectrics  is  very  noticeable. 

The  measurements  with  distilled  water,  as  before  stated, 
were  too  irregular  to  enable  one  to  decide  upon  the 
position  in  the  series  of  this  dielectric.  They  seem  to 
show,  however,  that  until  its  conductivity  has  been  in- 
creased, it  causes  an  increased  resistance  in  the  wire. 


28  SOME    OBSERVATIONS    UPON    THE 

Filled  with  distilled  water  at  1.45  p.  M.,  May 


DATE 

HOUR 

DIELECTRIC 

TEMP. 
24.4 

RESIST- 
ANCE IN 
OHMS 

May  17 

3.05  P.  M. 

Dist.  Water 

.  03444 

it       u 

3.55    " 

n 

25.0 

.03445 

it       u 

5.00    " 

tt 

26.0 

.  03445 

It               U 

6-00    " 

Air 

27.1 

.03475 

It           It 

8.00    " 

tt 

25.1 

.  03450 

"     18 

8.15A.M. 

tt 

21.0 

.  03403 

u       n 

9.25     " 

tt 

22.4 

.03418 

tt              tt 

10.06    " 

tt 

23.0 

.03427 

tt              tt 

10.15    " 

Dist.  Water 

21.1 

.03412 

It              It 

11.45    " 

tt 

23.1 

.03433 

"     19 

9.45    " 

Air 

22.0 

.03415 

Filled  tube  with  mixture  of  carbon  bi-sulphide  and  oil 
of  turpentine. 


RESIST- 

DATE 

HOUR 

DIELECTRIC 

TEMP. 

ANCE  IN 

OHMS 

Carbon     Bi-sul- 

May 19 

1  1 

10.45  A.  M. 
11.30     " 

phide  and  Tur- 
pentine Oil 

it 

23.8 
24.9 

.03432 
.03445 

CONDUCTIVITY    OF    A   COPPER    WIRE 


29 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

Carbon     Bi-sul- 

May  19 
ti 

12.15  P.  M. 
1.45       " 

phide  and  Tur- 
pentine Oil 
u 

25.7 
26.9 

.03454 
.03467 

a 

2.35      " 

it 

28.0 

.  03485 

K 

3.35      " 

u 

29.2 

.03500 

Regarding  the  conductivity  of  the  wire  in  air  as  unity, 
the  conductivity  in  the  liquids  examined  was  as  follows  : 

Petroleum                  -                  -                  -  1.0018 

Carbon  Bi-Sulphide  and  Oil  of  Turpentine  -    1.0009 
Carbon  Bi-Sulphide,  uncertain,  apparently       -        l.-f- 

Wood  Alcohol     -  -       .9998 

Benzine  -  .9994 

Wood  Alcohol  and  Beiizin<-  -       .9985 

Absolute  Alcohol      -  .9981 

Wood  Alcohol  and  Petroleum      -  -       .9973 

Distilled  Water,  uncertain,  apparently    -  1.— 

I  have  been  unable  in  the  limited  time  at  my  command 
to  find  any  fixed  relation  between  the  conductivities  of  the 
wire  in  the  various  dielectrics  and  any  other  known  prop- 
erties of  the  dielectrics.  The  tables  for  specific  inductive 
capacity  seem  to  me,  on  account  of  the  very  contradictory 
results  of  different  observers,  to  be  of  little  value,  and 
the  theoretical  relation  which  it  seems  should  exist 


30  SOME    OBSERVATIONS    UPON    THE 

between  the  specific  inductive  capacity  and  the  coefficient 
of  refraction  of  light  still  seems  to  be  contradicted  oftener 
than  it  is  verified  by  experiment.  In  the  hope  that  I 
might  find  some  relation  between  the  refractive  indices  of 
the  liquids  used  and  their  dielectric  properties  as  shown 
in  these  experiments,  I  had  the  refractive  indices  of  the 
same  liquids  determined  in  this  laboratory  by  Mr.  Mur- 
phy, a  very  careful  and  conscientious  observer.  Taking 
the  refraction  of  air  as  unity,  Mr.  Murphy  obtained  the 
following  results  for  the  D  line  : 

Petroleum,  poured  off  the  mixture  of  wood  alcohol 

and  petroleum    -  1.440 

Petroleum,  pure    -  1.435 

Benzine,  from  the  mixture  of  wood  alcohol  and 

benzine       -  1.405 

Benzine,  pure  1.403 

Absolute  Alcohol      -  1.363 

Wood  Alcohol  -     1.344 

Wood  Alcohol,  from  which  petroleum  had  been 

poured  off  1.340 

It  will  be  seen  at  once  that  the  order  of  arrangement 
of  the  liquids  is  very  different  in  the  two  tables.  While 
petroleum  has  the  highest  refractive  index  of  any  single 
liquid  used,  and  has  likewise  the  highest  place  in  regard 
to  the  dielectric  property  under  consideration,  absolute 
alcohol,  which  is  at  the  other  extreme  in  its  dielectric 
behavior  has  a  higher  refractive  index  than  the  wood 
alcohol,  which  differed  but  little  from  air  in  its  dielectric 
action  upon  the  wire. 


CONDUCTIVITY   OF   A   COPPER    WIRE  31 

I  hope  to  take  up  this  question  again  next  year  with 
increased  facilities  for  work,  and  to,  at  least,  accumulate 
data  in  regard  to  a  much  larger  number  of  dielectrics. 
There  are  several  other  important  questions  in  this  con- 
nection, the  answers  to  which  I  have  not  yet  had  time  to 
seek.  Among  them  may  be  mentioned  the  question  as 
to  the  influence  of  the  surface  condition  of  the  wire  used. 
In  the  experiments  which  I  have  thus  far  made,  the  sur- 
face of  the  copper  wire  was  much  oxidized.  I  hope  to 
repeat  some  of  the  same  experiments  with  a  polished 
wire,  and  with  wires  covered  with  various  insulators. 
The  influence  of  the  size  of  the  wire  also  remains  to  be 
studied.  Possibly,  by  this  means  one  may  be  able  to 
determine  whether  the  phenomenon  observed  is  due  to 
some  effect  throughout  the  body  of  the  dielectric,  or  is 
confined  to  the  surface  of  the  conductor.  The  effect  of% 
alternating  currents  through  different  dielectrics  will  also 
furnish  an  interesting  field  for  investigation. 

I  may  say  in  this  connection  that  I  have  several  times 
attempted  to  observe  similar  phenomena  with  wires  coiled 
in  various  ways,  and  measured  in  air  and  in  other 
dielectrics,  but  so  far,  I  have  found  a  definite  change  in 
resistance  only  when  the  current  was  sent  through  the 
tube  and  wire  as  previously  described.  In  using  a  coil 
of  wire  instead  of  the  tube  for  the  outer  conductor,  how- 
ever, the  resistance  is  so  much  increased  that  the  same 
change  in  resistance  would  not  be  noticeable  with  the 
apparatus  at  my  command. 


32  SOME   OBSERVATIONS    UPON   THE 


EFFECTS  OF  SOME  GASEOUS  DIELECTRICS 
UPON   CONDUCTIVITY 


Early  in  the  course  of  the  experiments  which  have 
been  described,  it  was  observed  that  after  pouring  out  the 
liquid  dielectric  some  time  was  required  for  the  resistance 
of  the  wire  to  return  to  its  normal  condition  in  air.  This 
suggested  the  thought  that  the  vapor  of  the  liquid  left  in 
the  tube  might  be  the  cause  of  this  phenomenon.  The 
following  experiments  were  accordingly  made  with  gas- 
eous dielectrics. 

The  first  gaseous  dielectric  definitely  tested  was  the 
burning  gas  used  in  the  laboratory.  This  gas  is  made 
from  gasoline  by  a  machine  on  the  grounds,  and  consists 
of  the  vapor  of  gasoline  mixed  with  air.  Its  sp.  g.  is 
somewhat  greater  than  air.  It  was  allowed  to  enter  the 
tube  direct  from  the  pipes  in  the  room,  arid  after  it  had 
driven  the  air  out  until  the  gas  was  coining  through 
freely,  the  tube  was  closed  and  the  measurements  were 
made.  The  first  series  of  measurements,  made  April  9th 
to  13th,  showed  that  the  resistance  in  the  gas  was  greater 
than  in  air,  but  the  measurements  in  both  dielectrics  were 
very  irregular.  Thinking  that  this  must  be  due  to  irreg- 
ularity in  the  contact  resistances,  the  apparatus  was  taken 
apart,  all  plugs  and  wire  contacts  were  carefully  cleaned, 
and  the  apparatus  was  again  connected  for  work.  The 
result  was  the  most  consistent  series  of  measurements 
made  at  any  time. 


CONDUCTIVITY    OF    A    COPPER    WIRE 


33 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  20 

8.  15  A.  M. 

Air 

16.3 

.03340 

tl    ti 

10.30     " 

« 

18.1 

.03364 

ft         ft 

11.30     " 

« 

18.1 

.03363 

ft          ft 

12.40  P.  M. 

« 

18.0 

.03362 

ft         tl 

3.55     " 

n 

19.8 

.  03383 

tt          ft 

5.40     " 

" 

19.4 

.03378 

It         ft 

7.45     " 

ti 

19.4 

.03378 

It        ft 

9.00     " 

n 

19.1 

.03374 

"    21 

8.05A.M. 

" 

17.5 

.03355 

ft        ft 

8.55     " 

" 

18.8 

.03372 

ft          tt 

10.00     " 

ft 

19.7 

.03382 

„   „ 

11.30     " 

tt 

21.1 

.03400 

12.10  P.  M. 

it 

21.9 

.03410 

tt        tl 

2.10     " 

n 

22.7 

.03420 

It        tt 

3.10     " 

it 

22.8 

.03420 

It        tl 

5.30     " 

ft 

22.0 

.03412 

11    22 

8.15  A.  M. 

n 

17.7 

.03357 

ft      ft 
3 

9.20     " 

ti 

18.8 

.03372 

34 


SOME   OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DlELECTKrC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  22 

10.15  A.M. 

Air 

19.4 

.03378 

((        « 

10.30     " 

Laboratory  Gas 

20.1 

.  03394 

a         « 

11.15    " 

u 

19.8 

.03390 

((        (( 

12.15  P.  M. 

(I 

19.7 

.03386 

U             « 

12.30    " 

a 

20.0 

.03393 

a         « 

1.30     " 

u 

21.0 

.  03403 

«        a 

3.10    " 

a 

21.9 

.03414 

u       « 

5.10    <( 

it 

22.9 

.  03427 

a       « 

7.00    " 

<.  i 

22.8 

.03426 

"  23 

7.25  A.  M. 

a 

12.0 

.03295 

«       u 

8.30     " 

u 

14.0 

.03320 

«       u 

9.00     " 

u 

15.0 

.03332 

«       u 

8.45  P.  M. 

u 

18.4 

.03372 

"  24 

7.40  A.  M. 

a 

15.3 

.03334 

«     a 

8.10     " 

u 

16.1 

.  03346 

«       a 

9.25     " 

u 

17.6 

.03362 

a       u 

11.00     " 

tl 

18.7 

.03377 

<i       u 

12.20  P.  M. 

(( 

18.8 

.03377 

CONDUCTIVITY   OF    A   COPPER    WIRE 


35 


The  gas  was  blown  out  by  air  at  1.40  P.  M.  and  the 
tube  allowed  to  stand  until  2.10,  when  air  was  again 
blown  through  it. 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

18.9 

RESIST- 
ANCE IN 
OHMS 

April  24 

3.00  P.  M. 

Air 

.03373 

<t      « 

5.40     " 

u 

19.2 

.03377 

«      n 

7.35    « 

11 

18.8 

.03370 

«     25 

7.15A.M. 

(4 

11.4 

.  03283 

«      « 

8.45    " 

ti 

13.8 

.03313 

«      « 

9.20    " 

C| 

14.4 

.03320 

«         a 

10.00    " 

« 

14.8 

.03322 

The  curves  representing  the  above  measurements  are 
shown  in  Fig.  3.  Of  the  17  measurements  in  gas,  only 
one  point  is  more  than  .00001  ohm  from  the  curve,  while 
the  nearest  distance  of  any  gas  point  from  the  air  curve 
is  equivalent  to  a  resistance  of  .00004  ohm,  and  the 
average  distance  of  the  gas  points  from  the  air  curve  is 
.000058  ohm.  This  would  make  the  resistance  of  the 
wire  in  gas  1.0017  times  its  air  resistance.  Without  mov- 
ing the  apparatus,  a  few  spoonfuls  of  sulphuric  ether  were 
poured  into  the  tube,  the  stop-cocks  closed  and  the  tube 
allowed  to  stand  until  it  was  filled  with  the  vapor. 


36 


SOME    OBSERVATIONS   UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

April  25 

12.00  M. 

Ether    Vapor 
and  Air 

15.8 

.03337 

it        tt 

1.50  P.  M. 

<( 

16.1 

.03348 

tl         tl 

3.10     " 

n 

17.0 

.03358 

ft         It 

3.55     " 

a 

17.6 

.03364 

(t         t( 

5.00     " 

a 

18.2 

.03373 

((         t( 

6.00     " 

it 

19.2 

.03384 

ft        It 

7.25     " 

it 

19.0 

.03382 

11      26 

7.30  A.  M. 

tt 

10.8 

.03282 

tt      it 

8.25     " 

tt 

12.8 

.03307 

it      it 

9.25     " 

« 

14.1 

.03323 

it      tt 

10.30     " 

it 

15.0 

.  03334 

tt      n 

12.00  M. 

tt 

15.4 

.03337 

tt      tt 

1.45  P.  M. 

tt 

16.2 

.03352 

The  above  measurements  compared  with  the  same  air 
curve  indicate  an  increase  of  resistance  due  to  the  ether 
vapor  of  .000083  ohm  or  .25  of  one  per  cent.  This  is  a 
greater  variation  than  was  given  by  any  single  liquid 
used.  After  the  ether  vapor  had  been  drawn  out  of  the 
tube  by  passing  a  current  of  air  through  it  for  more  than 
an  hour,  the  resistance  fell  but  little  from  the  above, 


CONDUCTIVITY    OF    A    COPPER    WIRE 


37 


showing  the  great  effect  due  to  a  very  small  quantity  of 
ether  vapor.  By  washing  the  tube  out  with  alcohol,  the 
resistance  of  the  wire  fell  to  nearly  its  former  value,  as 
shown  in  the  table  for  measurements  in  absolute  alcohol 
made  on  April  27th,  28th,  29th  and  30th,  and  which  were 
compared  with  the  same  air  curve  used  for  Fig.  3. 

The  effect  of  chloroform  vapor  is  shown  by  the  follow- 
ing table  : 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

EESIST- 

ANCE   IN 

OHMS 

May  4 

4.00  P.  M. 

Air 

22.1 

.  03428 

«         a 

5.55    " 

« 

21.2 

.03418 

«         « 

7.00     " 

« 

20.0 

.03404 

«         « 

9.00     " 

It 

18.9 

.03393 

"      5 

7.30  A.  M. 

ft 

14.9 

.03346 

«             U 

8.30     " 

it 

16.8 

.03370 

l(         11 

9.13     " 

ft 

17.9 

.03382 

11          (( 
((          (( 

9.35     " 
9.50     " 

« 

Chloroform  Va- 
por and  Air 

18.4 
19.0 

.03387 
.03397 

((          It 

10.20     " 

« 

19.2 

.03400 

«         « 

11.05     " 

u 

20.0 

.03412 

<«         « 

11.50    " 

« 

20.4 

.  03416 

(i         a 

12.30  P.  M. 

(( 

21.1 

.03423 

38 


SOME    OBSERVATIONS    UPON    THE 


])ATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

Chloroform  Va- 

May 5 

2.30  P.M. 

por  and  Air 

20.9 

.  03420 

«        u 

3.40     " 

tt 

20.2 

.03413 

it        n 

7.20     " 

1C 

18.4 

.03393 

In  the  above  measurements  the  tube  was  not  moved 
and  no  contact  was  disturbed  in  any  way.  Only  a  few 
teaspoonf uls  of  the  chloroform  were  poured  into  the  tube 
and  the  first  measurement  was  made  ten  minutes  after- 
ward. The  eight  measurements  made  in  each  dielectric 
are  thoroughly  consistent  and  indicate  an  increased 
resistance  in  the  chloroform  vapor  of  nearly  .17  of  one 
per  cent. 

A  few  measurements  made  in  the  vapor  of  carbon  bi- 
sulphide on  May  9th  showed  no  appreciable  difference 
from  the  air  resistance.  On  May  10th  an  attempt  \vas 
made  to  find  the  effect  of  rarefied  air  as  a  dielectric,  but  the 
apparatus  was  found  to  leak  air  so  badly  that  no  very 
near  approach  to  a  vacuum  could  be  reached  The 
measurements  marked  "  Vacuo  "  in  the  table  were  made 
while  the  tube  was  nearly  hermetically  sealed  and  a  large 
sized  Chapman  filter  pump  was  exhausting  the  air.  The 
water  pressure  upon  the  pump  was  very  heavy,  and  it 
would  exhaust  a  glass  tube  so  that  the  mercury  wrould 
rise  in  it  to  within  one  cm.  of  the  barometric  height.  It 
is  accordingly  probable  that  there  were  only  a  few  cm.  of 
air  in  the  tube.  It  is  probable,  however,  that  the  pressure 
was  not  the  same  for  the  different  measurements. 


CONDUCTIVITY   OF    A    COPPER    WIRE 


39 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  10 

11.10A.M. 

Vacuo 

21.1 

.03398 

«        « 

11.50 

11 

21.5 

.03402 

«          « 

1.20  P.  M. 

11 

22.0 

.03412 

«        (( 

1.35     " 

Air 

22.2 

.03408 

«        (( 

2.10     " 

(i 

22.7 

.03415 

u         a 

3.10    " 

Vacuo 

22.4 

.03414 

«        « 

3.25     " 

Air 

22.9 

.03418 

a         « 

4.15     " 

Vacuo 

22.9 

.03420 

«         « 

4.55     " 

Air 

23.4 

.03425 

«         a 

5.20     " 

Vacuo 

23.7 

.03428 

«         « 

5.50     " 

Air 

23.9 

.03428 

a         « 

7.30     " 

« 

23.0 

.03418 

"      11 

7.30  A.  M. 

« 

13.4 

.03304 

«         « 

8.10     " 

Vacuo 

14.5 

.03315 

it         « 

8.55     " 

Air 

15.6 

.03330 

«         « 

9.50     " 

M 

16.6 

.03343 

<(             U 

11.05     " 

ti 

17.2 

.03352 

ii         « 

12.30  P.  M. 

(t 

19.2 

.03375 

40 


SOME    OBSERVATIONS    UPON    THE 


DATE 

HOUR 

DIELECTRIC 

TEMP. 

RESIST- 
ANCE IN 
OHMS 

May  11 

2.15  P.  M. 

Air 

20.5 

.03391 

U            it 

4.15     " 

u 

22.0 

.03408 

The  air  measurements  all  lie  very  close  to  the  curve 
representing  the  average,  while  of  the  measurements  in 
rarefied  air,  all  but  one  indicate  an  increased  resistance, 
but  are  too  irregular  to  be  of  any  quantitative  value. 

Taking  the  conductivity  of  the  wire  in  air  as  unity, 
the  conductivities  in  the  other  gases  tested  are  approx- 
imately as  follows  : — 


Alcohol  Vapor    - 

Chloroform  Vapor 

Gasoline  Burning  Gas 

Sulphuric  Ether  Vapor  - 

Carbon  Bi-Sulphide  Vapor,  approximately, 

Rarefied  Air,  less  than         - 


.99949 
.99830 
.99820 
.99750 


1. 
•  1. 


I  am  not  aware  that  any  variation  in  the  dielectric 
properties  of  gases  corresponding  to  the  above  results 
have  ever  been  observed.  I  had  no  means  of  measuring 
the  refractive  indices  of  the  vapors  used,  and  of  thus 
computing  their  theoretical  specific  inductive  capacity. 
Taking  the  refractive  indices  as  given  by  Lorenz,  Landolt 
and  Bornstein's  Physikalisch-ChemischeTabellen,  Berlin, 
1883,  the  theoretical  specific  inductive  capacities  of  the 
vapors  used  are,  in  terms  of  air  : 


CONDUCTIVITY    OF    A    COPPER    WIRE  41 

Alcohol  Vapor  1.00120 

Chloroform  Vapor       -  -  1.00234 

Carbon  Bi-Sulphide  Vapor  -                                   1.00242 

Ether  Vapor  -  1.00321 

In  this  table,  the  alcohol,  chloroform  and  ether  vapors 
are  arranged  in  the  same  order  as  they  would  be  with 
reference  to  this  dielectric  property,  but  the  carbon  bi- 
sulphide vapor  is  not.  Probably,  no  value  should  be 
attached  to  this  comparison,  for  the  reason  that  the  vapors 
were  mixed  with  air  in  these  determinations,  and  their 
density  was,  perhaps,  very  different  from  that  at  which 
their  refractive  indices  were  determined. 

I  hope  to  pursue  these  investigations  much  farther 
during  the  coming  year,  and  to  accumulate  data  from 
which  it  may  be  legitimate  to  make  comparisons. 

JUNE  8,  1892. 


.03*  0 


0330 


/  TV 


.0330 


433 


YC   15219 


